154 QUALITATIVE ORGANIC ANALYSIS
earbazones, using a hydroxylamine salt in place of the hydrazine derivative.
Occasionally the oxime must be isolated by ether extraction. The following
procedure is adapted for water-insoluble compounds:
Dissolve 0.5 g. of hydroxylamine hydrochloride in 2-3 cc. of water, add
2 cc. of 10 per cent XaOH solution, 0.2 g. of the unknown, and exactly suf-
ficient alcohol to dissolve the organic compound. The oxime is generally
sparingly soluble and may crystallize from the dilute alcohol as it is formed.
Often it is best to warm the react ion-mixture on the steam-bath for 10 minutes,
using a condenser to avoid loss of solvent. If no sign of reaction is noted after
one hour, the mixture is diluted with 2 volumes of water and the precipitated
'. ] product tested to determine whether it is the oxime or the original unknown.
• \, The oximes are usually soluble in dilute alkali and may be reprecipitated by
* exact neutralization of the alkaline solution. Why is an excess of acid to be
I >• avoided?
*/*
4. Special Condensation Products.—Several of the most com-
mon carbonyl compounds (formaldehyde, acetaldehyde, and
acetone) are derivatized best by means of condensation reactions
other than those discussed above; the two aldehydes may be con-
densed with £-naphthol according to the directions outlined by
Mulliken, I, pages 23-25.
' Methylene-di-£-naphthol, m. 189-92°
/ Ethylidene-di-£-naphthyloxide, m. 172-3°
« The same derivatives can be applied to compounds like methylal
and acetal, which may be hydrolyzed to yield the above aldehydes.
' Acetone may be condensed (Claisen Reaction) with benzalde-
' hyde under the influence of alkali to yield dibenzylidene acetone,
//Q
\ C6H5CH=CH-C^-CH=CH-C6H5
£
m.p. 111-112°. Three drops of the ketone are dissolved in 2 cc.
\ of alcohol and 0.5 cc. benzaldehyde and 1 cc. dilute alkali added
i The mixture is heated to boiling for a minute, cooled, and then
\ agitated in order to cause the supercooled oil to solidify. Crys-
tallization from alcohol yields a pure material.
j 5. Oxidation Products.—Aromatic aldehydes are very readily
| oxidized to the corresponding acids; some of the members (ben-
? zaldehyde, for instance) are readily oxidized even by atmos-
' pheric oxygen. A general procedure outlined below for the oxi-
[ datiori of the side-chains of aromatic hydrocarbons is generally
j ; applicable to aldehydes also, except that only one-third of the-